Process for producing metallic materials containing thoria

ABSTRACT

The thoria used for the dispersion is obtained by pyrolysis of a chelated compound of thorium whose anion comes from a diketone Beta , this compound being preferably thorium acetylacetoneate.

United States Patent Office National DEtudes E! De RecherehesAerospatiales (par abreviation:

0.N.E.R.A.)

Chatillon-sous-Bagneux, France Assignee PROCESS FOR PRODUCING METALLICMATERIALS CONTAINING TI-IORIA 8 Claims, No Drawings Int. Cl C22c 39/50Field of Search 252/301 1;

[561 References Cited UNITED STATES PATENTS 2,099,325 6/1933 Zellman23/345 3,143,789 8/1964 ller 29/1825 3,159,908 12/1964 Anders 75/206 X3,278,281 10/1966 Ehringer.. 75/206 X 3,285,736 11/1966 Brinn 75/206 X3,310,400 3/1967 Alexander 75/206 3,422,167 1/1969 Bowman 23/3453,489,553 1/1970 Duletsky 75/206 FOREIGN PATENTS 1,232,353 1/1967Germany 75/206 39/5913 6/1962 Japan 23/345 Primary Examiner-Carl D.Quarforth Assistant ExaminerArthur J. Steiner Attorneys-Sylvester J.Liddy, John .1. Hart, Joe E. Daniels and Dayton'R. Stemple ABSTRACT: Thethoria used for the dispersion is obtained by pyrolysis of a chelatedcompound of thorium whose anion comes from a diketone [3, this compoundbeing preferably thorium acetylacetoneate.

PROCESS FOR PRODUCING METALLIC MATERIALS CONTAINING TI-IORIA The presentinvention relates, on the one hand, to metallic materials comprisingessentially a metallic mass (pure metal or alloy), called in terms ofthe art matrix, in the midst of which are incorporated, in the form of adispersed phase, fine particles of thoria (Th0,) whose presence improvesthe characteristics of the matrix, notably from the point of view of itsresistance to plastic deformation at high temperatures and from thepoint of view of its resistance to oxidation, and on the other hand, toprocesses for producing such metallic materials containing a dispersedphase of thoria. The invention is more particularly, but notexclusively, concerned with metallic materials of the type in questionand processes for their production, in which the matrix in which thethoria is incorporated is a refractory material (metal or alloy), and,in particular, a refractory material whose base consists of nickeland/or cobalt and/or iron; in addition, this matrix can possibly containaddition elements such as, in particular, chromium, zirconium, aluminum,titanium, tungsten, molybdenum, etc.

Before dealing with the principal feature of the invention, it isappropriate to mention that, in the past, the thoria incorporated in thematerials of the type in question was obtained by pyrolysis of certaincompounds of thorium (oxalates, nitrates, carbonates, hydroxides,etc...) which, even after a pyrolysis pushed up to high temperatures (ofthe order of l,000 C.), give a thoria accompanied by residues difficultto eliminate due to the fact that they are chemically bonded. In otherwords, by starting from these compounds of thorium, it was impossible toobtain, in simple and economical conditions, fine thoria sufficientlypure, the presence of chemically bonded residues compromising thehigh-temperature behavior of the metallic material containing adispersed phase of impure thoria.

The chief object of the invention is to provide materials and processesof the type in question that fulfill the various considerations ofpractice, and in particular, that no longer have the disadvantages,mentioned above, of the known materials and processes of the same typewhich use, for the production of the thoria for the dispersed phase,thorium compounds giving an impure thoria, that is to say accompanied byresidues altering the high-temperature behavior of the metallic materialfinally obtained containing the dispersed phase of thoria.

The invention consists, principally, in adopting, as the thoria which isto form the dispersed phase in the materials of the type in question,thoria obtained by pyrolysis of a chelated compound of thorium whoseanion comes from a diketone B, this compound being preferably thoriumacetylacetoneate, such a thoria being practically stoichiometric, thatis to say exempt of residues detrimental to the high-temperaturebehavior of the finally obtained metallic material containing thedispersed phase of thoria.

Apart from this principal feature, the invention comprises certain otherfeatures which are preferably used at the same time, and which will bemore explicitely described hereafter.

Preferred embodiments of the invention will now be described, merely byway of example. In these examples, the metallic material in question isa refractory metallic material having a matrix whose base is nickeland/or cobalt in which the thoria is dispersed in a homogeneous manner,thethoria being in an appropriately divided state (particles ofgranulation at the most of the order of0.l microns.) V

In accordance with the principal feature of the invention, one uses, asthe thoria which is to form the dispersed phase in the above-mentionedmatrix, thoria obtained by pyrolysis, at a temperature higher than 550C. and preferably lower than 900 C., of a chelated compound of thoriumwhose anion comes from a diketone B.

The thoria thus obtained has the advantage of being stoichiometric, thatis to say exempt of any residue, and particularly of water ofcrystallization or of OH groups, which is not the case with the thoriaobtained from other oxygenated compounds of thorium such as: oxalate,nitrate, hydrocur honate, hydroxide, etc...

Now, experience has shown that, if the thoria dispersed in a metallicmatrix containing nickel and/or cobalt is a thoria accompanied byresidues (in particular water of crystallization), the high-temperaturebehavior of this matrix is seriously compromised due to the fact that anuncontrolled dispersion of these residues takes place in the midst ofthe matrix; such a disadvantage is particularly serious when the metalmaterial containing nickel and/or cobalt and a dispersed phase of thoriais intended for the manufacture of pieces to be exposed to hightemperatures such as, in particular, blades, fixed or movable, of gasturbines.

The use, for the formation of a dispersed phase, of stoichiometricthoria obtained by pyrolysis of a chelated compound of thorium whoseanion comes from a diketone B avoids precisely the disadvantage,mentioned above, of refractory materials having nickel and/or cobaltcontaining a dispersed phase of a thoria obtained from thorium saltsother than a chelated compound of the type indicated.

The purity of the thoria obtained from such a chelated compound ofthorium can be explained, to a certain degree, by the fact that thechelated compounds in question, which are strong chelates, have only asmall propensity to form compounds of addition, and in particular,crystallize easily in the anhydrous state.

Among other chelated compounds of thorium whose anion comes from adiketone ,8, which chelated compounds can be used for the production ofa pure thoria, can be cited, in particular, thorium benzoylacetoneateand thorium dibenzoylmethanate, and above all, thorium acetylacetoneatewhich ap pears to be the most advantageous of the chelated compounds inquestion for the present purpose, that is to say for obtaining, in afinal material having a dispersed phase of thoria, a pure and finethoria in simple and economical conditions.

It seems appropriate, at this point of the description, to mention thatthe production of pieces formed of a refractory metallic material havinga dispersed phase of thoria conforming to the invention falls within thescope of conventional metallurgy of powders, that is to say of processesaccording to which an initial mixture of powders is first of allsubjected to a forming treatment, then to a sintering treatment.

Various embodiments of the invention will now be examined, which permitsuch an initial mixture of powders to be obtained (to which mixture atreatment of the metallurgy of powders will then be applied) in the mostinteresting case in which the matrix of the refractory material has abase of nickel and/or cobalt (i.e. the base consists of these two metalsor of only one of these metals) and in which the thoria dispersed inthis refractory material is pure and fine thoria obtained by pyrolysisof thorium acetylacetoneate, this initial mixture of powders being able,in the case envisaged, to contain nickel and/0r cobalt and such a pureand fine thoria, as well as possibly complementary constituents (otherthan nickel and/or cobalt) of the matrix.

For the purpose of simplifying the description, and also because it is apractically envisageable application of the invention, and hence canserve as an example, it will be supposed, in the following, that thematrix in which the pure and fine thoria is to be dispersed isconstituted exclusively of nickel and/or cobalt, the initial mixture ofpowders which has just been mentioned then being an intimate mixture ofpowders of nickel and/or cobalt (these metals being either codiffused ornot) and of thoria.

According to the first embodiment, in a first operational stage, thepure and fine thoria can be prepared by pyrolysis of thoriumacetylacetoneate at a temperature higher than 550 C. and preferablylower than 900 C. (this temperature being advantageously in theneighborhood of 700 C.); then an intimate mixture can be mechanicallyprepared of the pure and fine thoria thus obtained with some powder ofnickel and/or cobalt of fine granulation (grains of average dimensionsmaller than l0 microns and preferably of the order of 2 to 5 microns),this embodiment basically amounting to putting in presence and to mixingintimately in a mechanical manner two solid phases formed respectivelyby the powder of pure and fine thoria and the powder of nickel and/orcobalt.

A quantitative example according to this first embodiment will now begiven.

EXAMPLE 1 (matrix formed of nickel) a. Preparation of the thoriumacetylacetoneate.

Fifty grams of thorium nitrate, Th (NO .6H,O, are dissolved in one litreof water.

Ammonia liquor is added until a pH of the order of is obtained, whichhas the effect of making the thorium hydrate precipitate.

This thorium hydrate is washed and filtered on a very fine fabric, afterwhich a final washing is carried out with ethyl alcohol.

The last traces of water are eliminated by means of ternaryalcohol-benzine-water azeotrope by addition to the filtrate of one litreof ethyl alcohol at 95 percent and of 600 cm. of benzine, after whichthe product is dried at 60 C. until three-fourths of the solution hasevaporated.

Acetylacetone is added until complete dissolution is reached.

The product is dried, which has for its effect to crystallize thethorium acetylacetoneate Th(C -,l-l O which is then ground in a mortarso as to obtain a powder whose color is yellow.

b. Pyrolysis of the thorium acetylacetoneate.

The thorium acetylacetoneate thus obtained is placed in a nickelcontainer and heated in an oven at 600 C. for a duration of aboutone-half hour, this treatment having the effect of causing the fusion ofthe thorium acetylacetoneate which then blisters to give finally a pureand very friable thoria foam.

c. Mechanical incorporation of the thoria in the nickel powder.

In a ball mill comprising a nickel vat of about 4 litres half full ofnickel balls of about 12 millimeters in diameter, there are introduced 2kilograms of very pure and very fine nickel powder coming from thepyrolysis of nickel carbonyl (granulation of from 2 to 5 microns), 60grams of thoria obtained as indicated above under (b) and 850 cm. ofbenzine.

The grinding is continued for 24 hours and the product is thencentrifuged, dried in a drying oven at 80 C. and calcined in hydrogen at850 C. for one hour.

An intimate mixture of powders of nickel and of pure and fine thoria isthus obtained, and this mixture will then be subjected to a treatment ofmetallurgy of powders to produce refractory pieces of nickel containinga dispersed phase of thoria, which are the pieces originally intended tobe produced.

It is appropriate to mention that the process described with respect tothis Example I is entirely applicable in the case in which the matrix isconstituted of cobalt or of a nickel-cobalt alloy.

Although one can hope to obtain satisfactory pieces by this embodiment,it must nevertheless be admitted that it is difficult to obtain, merelyby mechanical means, an intimate mixture with homogeneous dispersion oftwo solid phases having very fine granulation, and there is a risk thatthe dispersion of ,the thoria will not have a maximum homogeneity.

Thus, it seems preferable to use one of the two embodiments which willnow be described, and which have this common characteristic of bringinginto play at least one liquid phase for the preparation of the mixtureof powders, and of forming the pure and fine thoria in situ, that is tosay in the presence of the powder of powder of nickel and/or cobalt orof a compound of nickel and/or of cobalt from which such a powder ofnickel and/or cobalt can be obtained; these two embodiments have theconsiderable advantage, due to the fact that they bring into play atleast one liquid phase, of avoiding the constraints inherent in thefirst embodiment and of consequently assuring an absolutely homogeneousdispersion of the thoria.

Thus according to the second embodiment of the invention, a liquid phase(containing the thorium) is put in the presence of solid phase(containing the metal in the present case, nickel and/or cobalt). To dothis, advantageously, a solution of thorium acetylacetoneate is used towet a fine powder of nickel and/or cobalt or a compound of nickel and/orcobalt adapted to give a nickel oxide and/or a cobalt oxide reducible bypyrolysis effected in the relatively low temperature zone suitable forthe formation of pure and fine thoria by pyrolysis of thoriumacetylacetoneate.

As solvent for the thorium acetylacetoneate, one can use, in particular,ethanol, acetone, ether, and better still, acetylacetone.

The wetting thus achieved permits an intimate mixture of theconstituents to be obtained, and the pyrolysis effected afterwards at atemperature comprised between 550 C. and 900 C. has the effect oftransforming the thorium acetylacetoneate into pure and fine thoria, andwhen the starting product is a powder of a compound of nickel and/orcobalt, of transforming this compound directly into metal (the case inwhich the starting products are oxalates for example) or again intooxides reducible in hydrogen (the case in which the starting productsare carbonates for example).

A quantitative example of this second embodiment of the invention willnow be given.

EXAMPLE II Three kilograms of oxalate of nickel and/or cobalt areintroduced into a mixer provided with a heating device (for example aWERNER mixer), and there is incorporated by rotation into this coldoxalate, 64 grams of thorium acetylacetoneate dissolved in 900 cm. ofacetylacetone.

The cold mixing is continued for one hour, then the temperature isprogressively raised to C., which causes the volatilization of thesolvent by ceaselessly renewing the surface contacts.

The dry powder thus obtained is placed in a nickel container andintroduced into an ajustable temperature oven capable of bringing thispowder to a temperature of the order of 500 C. in 4 hours in ordinaryatmosphere, after which this temperature is maintained for 1 hour. Aftercooling, the powder is placed in a nickel cup and the pyrolysis iscarried out in dry hydrogen at 700 C for 2 hours.

An intimate mixture is thus obtained of powders of nickel and/or cobaltand of pure and fine thoria dispersed in a homogeneous manner, thismixture being suitable as the initial mixture for a subsequent treatmentof the metallurgy of powders.

Finally, according to a third embodiment, two liquid phases are put inthe presence of one another, these two liquid phases containingrespectively the thorium and the metal (in this case, nickel and/orcobalt); to do this, advantageously, thorium acetylacetoneate in themelted state is mixed with some acetylacetoneate of the metal or of themetals also in the melted state, these two compounds being miscible inall proportions.

Then a simultaneous pyrolysis is carried out of the two compounds thusmixed, which leads to a pure and fine thoria excellently dispersed inthe powder of nickel and/or cobalt.

To finish, a quantitative example of this third embodiment will now begiven.

EXAMPLE III a. Preparation of the acetylacetoneate of nickel and/or ofcobalt.

One hundred grams of nitrate of nickel and/or of cobalt are dissolved in500 cm. of water, and a solution of 50 grams of ammonium carbonate in500 cm. of water is added.

A precipitate of carbonate of nickel and/or of cobalt is thus obtainedwhich is washed, centrifuged and dried, then incorporated progressivelyinto 200 cm. of boiling acetylacetone, which permits, after evaporationof the excess acetylacetone, crystals of metallic acetylacetoneate ofnickel and/or of cobalt, or again mixed crystals of acetylacetoneate ofnickel and of cobalt, to be obtained.

b. Mixture of the acetylacetoneates of nickel and/or of cobalt and ofthorium.

A mixture formed by one kilogram of acetylacetoneate of nickel and/or ofcobalt, 17 grams of thorium acetylacetoneate and 750 cm. ofacetylacetone are heated to ebullition.

When the solution becomes very viscous, it is placed in a vacuum dryerwhere the evaporation is continued at 150 C. A foam is thus obtainedwhich is then treated like the dry powder of Example II.

In any case, and whatever embodiment is adopted, an initial mixture ofpowders is provided which has, for the production of refractory pieceshaving a base of nickel and/or of cobalt containing a dispersed phase ofthoria, the advantages (explained previously) inherent in the purity andthe fineness of the thoria used, and the initial mixture of powders inquestion lends itself to all the conventional operations of themetallurgy of powders (forming, sintering, sheathing, hot drawing, coldworking, etc...).

Moreover, in the case of the second and third embodiments, an excellentdispersion of the pure and fine thoria is assured in the constituent ofconstituents of the matrix, due to the fact that this thoria is formedin situ and by a process (forming an essential part of the invention)bringing into play compounds of thorium whose pyrolysis is achieved atrelatively low temperatures (of the order of 550 C. for thoriumacetylacetoneate); this permits pollution to be avoided of the metallicphase and correlatively of the thoria by reaction with that pollutedmetallic phase, which is very advantageous, since any pollution would bedisastrous for the refractory metallic product containing the dispersedphase of thoria.

Although the present invention has been described with particularreference to particular embodiments, it should be understood that theinvention should not be limited thereto, as there might be variousmodifications made without departing from the scope or spirit of thisinvention.

What we claim is:

1. In a process of producing a sintered metallic material having as itsbase at least one metal powder and containing a dispersion of thoria,the steps of, supplying a chelated compound of throium whose anion comesfrom a l! diketone, pyrolyzing said chelated compound of thorium toprepare said thoria, intimately mixing said thoria with at least onesaid metal powder forming the base of said metallic material, andsubsequently processing the mixture by powder metallurgy.

2. A process according to claim 1 which comprises intimately mixing aliquid phase containing said chelated compound of thorium with a solidphase containing at least one said metal, and pyrolyzing said mixture.

3. A process according to claim 1 which comprises intimately mixing afirst liquid phase containing said chelated compound of thorium with asecond liquid phase containing at least one said metal, and pyrolyzingsaid mixture.

4. A process according to claim ll wherein said chelated compound ofthorium is thorium acetylacetoneate, and said pyrolysis if effected at atemperature in the range 550 C. to 900 C.

5. A process according to claim 4 wherein said thorium acetylacetoneateis pyrolyzed at a temperature in the neighborhood of 700 C. to form afoam of thoria in the solid state, and said solid state thoria isintimately mixed by grinding with a powder containing at least one saidmetal chosen from the class consisting of nickel and cobalt.

6. A process according to claim 2 wherein said liquid phase is asolution of thorium acetylacetoneate in an appropriate solvent, and saidsolid phase is a powder containing at least one said metal chosen fromthe class consisting of nickel and cobalt.

7. A process according to claim 6 wherein said solvent is acetylacetone,and said pyrolysis is effected at a temperature in the range 500 C. to900 C.

8. A process according to claim 3 wherein said first liquid phasecomprises thorium acetylacetoneate and said second liquid phasecomprises an acetylacetoneate of at least one said metal chosen from theclass consisting of nickel and cobalt.

2. A process according to claim 1 which comprises intimately mixing aliquid phase containing said chelated compound of thorium with a solidphase containing at least one said metal, and pyrolysing said mixture.3. A process according to claim 1 which comprises intimately mixing afirst liquid phase containing said chelated compound of thorium with asecond liquid phase containing at least one said metal, and pyrolysingsaid mixture.
 4. A process according to claim 1 wherein said chelatedcompound of thorium is thorium acetylacetoneate, and said pyrolysis ifeffected at a temperature in the range 550* C. to 900* C.
 5. A processaccording to claim 4 wherein said thorium acetylacetoneate is pyrolysedat a temperature in the neighborhood of 700* C. to form a foam of thoriain the solid state, and said solid state thoria is intimately mixed bygrinding with a powder containing at least one said metal chosen fromthe class consisting of nickel and cobalt.
 6. A process according toclaim 2 wherein said liquid phase is a solution of thoriumacetylacetoneate in an appropriate solvent, and said solid phase is apowder containing at least one said metal chosen from the classconsisting of nickel and cobalt.
 7. A process according to claim 6wherein said solvent is acetylacetone, and said pyrolysis is effected ata temperature in the range 550* C. to 900* C.
 8. A process according toclaim 3 wherein said first liquid phase comprises thoriumacetylacetoneate and said second liquid phase comprises anacetylacetoneate of at least one said metal chosen from the classconsisting of nickel and cobalt.